The positive securement or attachment of electrodes to internal body organs has been accomplished in several ways. With respect to the heart, for example, electrode placement and attachment has been effected transvenously as well as transthoracically.
The transvenous approach has as its purpose an electrical contact with or into the endocardium by extension of the lead through the vein system of the heart to the output terminals of an implanted pulse generator. Dependent upon the purpose of the contact, the desired position of the electrode may be within the ventricle, atrium, or atrial appendage of the heart. Positioning is accomplished through the use of fluoroscopy, or other similar techniques, and is an inexact art, at best. Attachment often is not positive in that the electrode is positioned at a reasonably stable position, e.g., the right atrial appendage in the hope that the electrode will remain in position until it is secured through a natural buildup of fibrotic tissue. In an effort to hold the electrode in position pending the buildup of fibrotic tissue, some prior art transvenous electrodes have been provided with mechanical devices for engagement with the heart tissue, particularly the trabeculae of the right atrial appendage. Such a prior art transvenous electrode is disclosed in U.S. Pat. No. 3,902,501.
The transthoracic approach has as its purpose a positive epicardial or myocardial electrical contact. The configuration of most prior art electrodes of this type required a thoracotomy for positioning and attachment, particularly to the atrium or atrial appendage. The sutureless myocardial lead disclosed in U.S. Pat. No. 3,737,579 has its primary application to the ventricular attachment. The atrium for the most part is relatively thin-walled and incapable of accepting the sutureless myocardial lead. The exterior of the atrial appendage is rather convoluted and does not afford an acceptable surface or angle of approach for this lead.
From the above, it can be seen that the more accurate positioning and positive securement available with a thoracotomy carries with it a much greater patient risk. While the risk to the patient is significantly less with a transvenous approach, the positioning of the electrode and its securement are much less certain.